Small businesses in the Back Bay that suffered financial losses because of the Boston Marathon bombings will be able to apply for federal loan assistance, the US Small Business Administration said late Friday.

The agency, responding to a request from Massachusetts Governor Deval Patrick, issued a special declaration for Suffolk County Friday that would allow the federal government to provide low-cost loans to stores and other companies affected by the April 15 attacks.

Boston officials said that while only a relatively few storefronts were physically damaged in the blasts, as many as 500 businesses lost money in the 12-block section of Boylston Street that was cordoned off by the FBI as a crime scene. Some sections remained off limits for more than a week as investigators scoured the street, sidewalks, and even rooftops for evidence.

Aram Boghosian for The Boston Globe

Governor Deval Patrick.

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“We’re looking at millions of dollars in losses,” said Meg Mainzer-Cohen, president of the Back Bay Association, a group that represents businesses. “Some of it can be recouped by the passionate support we’re receiving now. But there are some that, no matter what, won’t be able to make it up.”

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The city has asked businesses to self-report their loss estimates by comparing revenue from the 2012 Marathon week to this year. No estimates have been made of the total economic impact on the neighborhood, but officials said Friday that the 10 most heavily affected businesses reported an aggregate loss of $2.3 million.

Whiskey’s Smokehouse on Boylston estimated its losses would exceed $250,000. General manager Becky Caloggero said she’s waiting to see how much the restaurant’s insurance company provides for interruption of service before deciding whether to seek a federal loan.

Sugar Heaven, a candy shop two blocks away, said it probably lost $65,000. The Stephanie’s on Newbury was closed just three days, but that was enough to cost about $200,000 in revenue, the restaurant’s operations manager said earlier this week.

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“For some businesses, this was their week, their biggest week,” said Sheila Dillon, director of the the city’s Department of Neighborhood Development.

Michael Lampton, an SBA spokesman, said small businesses that were in the blocked-off zone and that can show they suffered financial losses will qualify to borrow money. Loans of up to $2 million will be available, at a fixed interest rate of 4 percent over 30 years.

For many businesses, a lack of cash has become an emergency — they need money now for rent and payroll or to restock shelves. Lampton said those businesses should be able to receive checks within 10 days of applying for funds.

“It will give them an infusion of cash flow that will allow them to meet their bills until they are fully up and running again,” Dillon said.

President Obama earlier issued an Emergency Declaration for Suffolk, Norfolk, and Middlesex counties.

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That designation authorizes the federal government to reimburse communities, state agencies, and some nonprofits for certain emergency costs.